feat: webContents.loadURL returns a promise (#15855)

lib/browser/navigation-controller.js

@@ -63,9 +63,66 @@ const NavigationController = (function () {
     if (options == null) {
       options = {}
     }
+    const p = new Promise((resolve, reject) => {
+      const resolveAndCleanup = () => {
+        removeListeners()
+        resolve()
+      }
+      const rejectAndCleanup = (errorCode, errorDescription, url) => {
+        const err = new Error(`${errorDescription} (${errorCode}) loading '${url}'`)
+        Object.assign(err, { errno: errorCode, code: errorDescription, url })
+        removeListeners()
+        reject(err)
+      }
+      const finishListener = () => {
+        resolveAndCleanup()
+      }
+      const failListener = (event, errorCode, errorDescription, validatedURL, isMainFrame, frameProcessId, frameRoutingId) => {
+        if (isMainFrame) {
+          rejectAndCleanup(errorCode, errorDescription, validatedURL)
+        }
+      }
+
+      let navigationStarted = false
+      const navigationListener = (event, url, isSameDocument, isMainFrame, frameProcessId, frameRoutingId, navigationId) => {
+        if (isMainFrame) {
+          if (navigationStarted) {
+            // the webcontents has started another unrelated navigation in the
+            // main frame (probably from the app calling `loadURL` again); reject
+            // the promise
+            return rejectAndCleanup(-3, 'ERR_ABORTED', url)
+          }
+          navigationStarted = true
+        }
+      }
+      const stopLoadingListener = () => {
+        // By the time we get here, either 'finish' or 'fail' should have fired
+        // if the navigation occurred. However, in some situations (e.g. when
+        // attempting to load a page with a bad scheme), loading will stop
+        // without emitting finish or fail. In this case, we reject the promise
+        // with a generic failure.
+        // TODO(jeremy): enumerate all the cases in which this can happen. If
+        // the only one is with a bad scheme, perhaps ERR_INVALID_ARGUMENT
+        // would be more appropriate.
+        rejectAndCleanup(-2, 'ERR_FAILED', url)
+      }
+      const removeListeners = () => {
+        this.webContents.removeListener('did-finish-load', finishListener)
+        this.webContents.removeListener('did-fail-load', failListener)
+        this.webContents.removeListener('did-start-navigation', navigationListener)
+        this.webContents.removeListener('did-stop-loading', stopLoadingListener)
+      }
+      this.webContents.on('did-finish-load', finishListener)
+      this.webContents.on('did-fail-load', failListener)
+      this.webContents.on('did-start-navigation', navigationListener)
+      this.webContents.on('did-stop-loading', stopLoadingListener)
+    })
+    // Add a no-op rejection handler to silence the unhandled rejection error.
+    p.catch(() => {})
     this.pendingIndex = -1
     this.webContents._loadURL(url, options)
-    return this.webContents.emit('load-url', url, options)
+    this.webContents.emit('load-url', url, options)
+    return p
   }
 
   NavigationController.prototype.getURL = function () {